1. Field of the Invention
This invention relates to an endless chain to be lapped around a rotational drive member and a driven member for power transmission as by a silent chain, chain belt or the like.
2. Prior Art
The chains for silent chains or chain belts are generally constituted by endlessly connected link plate groups which consist of a plural number of link plates each with a pair of pin-receiving holes, and successively connected with a shift of one pitch from adjacent groups and with the respective link plates intermeshed alternately with the link plates of the latter, by means of paired rocker pins of sectionally arcuate shape inserted in the pin-receiving holes of the intermeshed link plates in back-to-back relation with each other. The chain is lapped around a rotational driving member such as a sprocket or pulley and a driven member to transmit power from the driving to driven member.
Since the chain is lapped around a rotational member as mentioned above, the adjacent link plate groups which are connected by the rocker pins should be flexible relative to each other in order to ensure smooth lapping of the chain. For this purpose, the paired rocker pins are inserted in the pin-receiving holes in contact with each other in back-to-back relation to permit rolling movements of the respective pins, namely, to permit flexion between the adjacent link plate groups. The range of the flexing movements of the link plate groups varies depending upon the radius of curvature of large arc portions which form the back sides of the respective rocker pins. The range of the relative rolling movements is broadened by minimizing the radius of curvature of the large arc portions, permitting flexing movements of a broader range between the adjacent link plates groups.
In this connection, it is advantageous from the standpoint of power transmission efficiency to enlarge the radius of curvature of the arcs of the rocker pins. Besides, a larger radius of curvature is advantageous in that the Hertz stress can be suppressed, permitting one to reduce the frictional wear in contacting portions of rocker pins for protection thereof.
Therefore, it has been the usual practice in the prior art to limit the afore-mentioned flexing movements of rocker pins to a range which is necessary for smoothly lapping the chain on rotational members, for the purpose of enhancing the efficiency of power transmission.
However, in case the relative flexing movements of the link plate groups is suppressed to a minimum necessary range for lapping the chain around the drive and driven members, the respective link plate groups of a chain become unable to flex in the reverse direction or their inverse flexing movements are restricted to a considerable degree. If such a chain is used under a condition involving large torque fluctuations, vibrations or noises are generated by unduly large forces which are imposed on the chain due to limitation of the inverse flexing movements between the respective link plate groups. There arises another problem that extremely high stress is generated between link plates and rocker pins which are held in lock-up state, accelerating their fatigue and inducing ruptures at an early stage. Further, a chain to be rotated at high speed is usually provided with a tensioner therealong. However, it becomes necessary to use a tensioner of a small radius of curvature in a case where the inverse flexing movements are limited as mentioned hereinbefore, resulting in a failure of taking up slack of the chain by the tensioner or extremely large restrictions in its layout.